This project will define how hypercapnia (increased carbon dioxide concentrations) modifies oxidant-mediated inflammatory pathways with in vitro and in vivo models of inflammatory lung injury. Inflammatory-mediated lung injury often damages the air-blood barrier, impairing gas exchange and inducing hypoxemia. Recent innovative clinical strategies for resolving this pathologic process include the use of "protective" low tidal volume ventilatory strategies to retard ventilator-associated lung injury (VALI). There is an increasingly pervasive clinical perception that the allowance of hypercapnia is desirable and may be utilized as a strategy unto itself to retard lung injury. While there is modest clinical evidence that supports this approach, it remains biochemically unsubstantiated. In contrast, there is expanding evidence that CO2 actively reacts with inflammatory oxidants, yielding products with altered oxidizing and nitrating capabilities. We have observed that carbon dioxide rapidly reacts with reactive oxygen species generated during systemic inflammation, forming reactive nitrating and oxidizing species, specifically nitrosoperoxocarbonate (ONOOCO2-) a species capable of mediating further potent oxidation and nitration reactions. From this foundation of knowledge, it is hypothesized that hypercapnia amplifies inflammatory lung cell injury via modulation of oxidative injury and signaling pathways. To test this hypothesis, the following Specific Aims will be pursued: #1: Define the influence of hypercapnia on oxidant generation and cell signaling pathways in an in vitro model of lung epithelial and endothelial cell inflammation. #2: Investigate the contribution of mechanical stress, in conjunction with hypercapnia, on oxidative inflammatory and cell signaling events in an in vitro model of lung injury. #3: Delineate the consequences of concurrent hypercapnia, lung cell mechanical stress, and inhaled .NO in an in vivo model of critical illness. This proposed experimental plan advances recent investigation of CO 2interactions with [unreadable]NO-derived species by examining the influence of CO2 on in vitro and in vivo models of inflammatory and ventilator-induced lung injury. The proposed research plan also provides a key element of the training platform that has been devised for the further development of the candidate as a physician-scientist and his pursuit to understand and improve issues of relevance to critical care medicine.